ipi6 



BETTER FRUIT 



Page IS 



Spot Diseases of the Apple Causing Much General Confusion 



liv (;iiarles l!rooks and D. F. Fisher, U. S. Department of ARricuItiiro. Read liy Mr. I'ishcr before the Wasliington State Horticultural Association. 



THERE is so much general con- 

 fusion in regard to the nature, 

 cause and niettiod.s of treatment of 

 the various spot (hseases of the apple 

 that it has seemed desirable to present 

 a progress report of our studies of tliese 

 diseases. While we still have very 

 much to learn about these various 

 troubles, it is hoped that what we have 

 already found out may prove of value 

 to the liorticidturist and help him to 

 distinguish between the different dis- 

 eases, that he may shape his control 

 measures accordingly. The disease 

 known as bitter pit is referred to under 

 various names. The Germans were the 

 first to describe the disease and called 

 it "stippin." This name is now in quite 

 geneial use in New York State. In the 

 United Stafes the disease was first re- 

 ferred to as Baldwin Sijot, since the 

 Baldwin was found particularly suscep- 

 tible to it in New En.nland. This name 

 was first used in Vermont and is in 

 quite general use throughout the 

 country. The disease has been re- 

 ferred to in New Hampshire and Ore- 

 gon puljlicalions as "fruit pit." In 

 England, South .Africa and Australia 

 the disease is known as "bitter pit." 

 This term has also been quite gener- 

 ally used in the correspondence of the 

 U. S. Department of Agriculture. The 

 term "pit" seems much better suited to 

 describe the (hsease than that of "spot," 

 since it is set off from a number of 

 fruit spots by a definite ijitling or 

 depression of the apple surface. It 

 also seems desirable to eliminate the 

 word "Baldwin." since to use it con- 

 veys the im])ression that the disease 

 might be confined to the Baldwin vari- 

 ety, whereas [he (Irimes, Northern Spy, 

 Yellow BelHlower and other varieties 

 are just as susceptible as the Bnlilwin. 

 This disease has received more atten- 

 tion in recent years than formerly, 

 partly because the other diseases have 

 been brought largely under control by 

 spraying, partly because there is a 

 greater demand for high-grade fruit of 

 good keeping quality, and partly be- 

 cause the methods that have been 

 adopted for producing extra fancy 

 apples tend to increase rather than 

 decrease this jiarficular trouble. It has 

 been extremely (Hdicult to find out the 

 cause of tiie disease. In the first place, 

 it is of ])liysiologi( ;d nature, and its 

 occurrence is determined by the .gen- 

 eral condition of the tree and fruit, and 

 such general factors as these are hard 

 to control in a way to get definite data. 

 Secondly, there has been a great deal 

 of confusion in regard to the disease 

 because there are a number of very 

 similar spots that have l)een referred 

 to under the ai)ove names, but which 

 differ from one another in nature, 

 cause and means of control. This 

 makes any general statement in regard 

 to the disease of questionable value 

 unless there is a careful description 

 given of the trouide under discussion. 

 Among these similar spots are the 



"Fruit Spot," ".lonathan Si)ot," "Stig- 

 monose," true bitter pit, and the corky 

 pit, or so-called "droutli spot." The 

 fruit spot is characterized by hard, 

 sunken, green or red s))ots with inimer- 

 ous black specks scattered over the 

 sunken area. It is a fungous disease 

 and is readily controlled by spraying 

 with fungicides. It has never been 

 reported west of the Rocky Mountains, 

 and so far as Washington State is con- 

 cerned, the disease can be left out of 

 consideration. In spite of this fact, in 

 some cases orchardists in the W'est 

 have carried on extensive spraying 

 work for the control of bitter pit, fol- 

 lowing up the Eastern directions for 

 fruit spot, and thinking they were 

 fighting the same disease. 



Jonathan Spot is the name applied to 

 very shallow black or brown spots in 

 the skin of the apple. In late stages 

 the spots may become sunken and part 

 of the adjacent flesli inv(dved. Various 

 fungi may gain entrance and hasten the 

 enlargement of the s]K)ts. In the West 

 this disease is not generalh confused 

 with bitter pit. In some (|uarteis it has 

 been attributed to arsenical spray in- 

 jury, but this theory of tlie cause of the 

 trouble has been definitely (fisproved 

 by the extensive spraying experiments 

 which the Department of Agriculture 

 conducted in the State of Delaware in 

 1910 and 1911. Blocks of .lonathans 

 were sprayed with different amounts of 



lead arsenate to see if the prevalence 

 of the disease could be correlated with 

 the amount of leard arsenate used in 

 the spray. Data was secured on the 

 disease both at the time of picking and 

 after several weeks in storage. No cor- 

 relation whatever could be found be- 

 tween the arsenate of lead and the 

 disease. In many cases there was more 

 disease on fruit whicli had not been 

 sprayed at all than upon that which 

 had received the heaviest application of 

 lead arsenate. The disease is of a 

 physiological nature, and is essentially 

 a storage trouble, and therefore is not 

 controllable by spraying. It is greatly 

 reduced by hastening the fruit to cold 

 storage. Our experiments with this 

 disease seem to indicate that factors 

 similar to those involved in the cause 

 and control of bitter pit are closely 

 paralleled in the case of Jonathan spot. 

 These will be taken up in more detail 

 in the consideration of bitter pit. Jon- 

 athan spot does not seem to be a de- 

 sirable name for this trouble, since it 

 implies that llie disease is largely con- 

 fined to the Jonathan variety, whereas 

 Spitzeiiberg, Yellow Newtown and 

 other varieties are often as badly 

 affected. In the interest of clearness 

 it would be desirable to eliminate, if 

 we could, the name of any particular 

 variety of fruit from the names of 

 diseases. The term "freckles" has been 

 applied to Jonathan sjiof, but it has not 



Heavily 

 irrigated 

 all season. 



Moderate 

 irrigation. 



Moderate 

 irrigation uulil 

 .-Vugust 1, then 

 lieavy until 

 September 10. 



Light 

 irrigation. 



Y///////////////// 



Soil moisUu'P. 



liillir pil. 



Chart showing corrclalion hclwccn soil moisture and billcr pil in l!>l.'i 



at Wcuatchcc, Wasliiiigl.in, 



i-nts on Grimes 



